It will be appreciated that engines, and in particular, aircraft engine components, such as electrical or electronic devices and/or static structural parts, must be cooled in order to remain within acceptable operational temperature ranges etc. Cooling with regard to aircraft engines can be achieved through utilisation of ambient airflow bypass through the engine utilising a heat exchanger and the differential between the cooler bypass side and the hot engine side of the exchanger. Bypass ambient air cooling is conventionally used for cooling an engine when the temperature differential and available heat exchanger area are adequate. It will be understood with regard to aircraft in particular, there are limitations upon the available heat exchanger area due to weight and volume accommodation problems.
Additionally with regard to aircraft engines, there are two differing cooling scenarios. Firstly, when the aircraft engine is operating at altitude and in a cruise state, it will be understood that the ambient air temperature, that is to say outside of the engine will be relatively cool creating a significant temperature differential and similarly, the bypass airflow rate will be at a reasonably high speed for cooling purposes. However, in a second cooling scenario when the engine is idling prior to take off, that is to say on the ground, there will be a relatively high ambient temperature and limited airflow for cooling. In such circumstances, in order to accommodate for this second scenario, it is necessary to provide significantly greater cooling capacity than strictly necessary for normal operation of the aircraft and engine at altitude. This additional cooling capacity adds to engine weight and operational complexities.